High temperature superconducting (HTSC) compounds including mixed oxides of rare earth, alkaline earth and copper metals are known (e.g., Phillips). Wu et al., and Hor et al. have discussed Y--Ba--Cu--O compound systems as exhibiting HTSC. Moodenbaugh et al., Murphy et al., and Hor et al. disclose additional rare earth, alkaline earth, copper metal mixed oxide compounds exhibiting superconductive properties. Additional superconducting mixed metal oxide compounds of La--Sr--Cu--O, Bi--Sr--Ca--Cu--O and Tl--Ba--Ca--Cu--O have also been developed.
Tarascon et al. disclose Bi--Sr--Ca--Cu--O superconducting compounds of the formula Bi.sub.2 Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.y wherein n=1, 2 or 3 which are prepared by firing at high temperatures stoichiometric amounts of Bi.sub.2 O.sub.3, SrCO.sub.3 or SrO.sub.2, and CuO powders. Similarly, Chakoumakos et al. have disclosed the preparation of Bi--Sr--Cu--O compounds, particularly Bi.sub.2 Sr.sub.2 CuO.sub.6 compounds of the formula Bi.sub.2 Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x, where n is from 1 to 5 which are formed by molecular beam epitaxy of layered structures. Eckstein et al. have also disclosed the formation of thin films of perovskite-related high-temperature superconductors using atomic layer molecular beam epitaxy.
One of the major goals in the technology of thin high-temperature superconducting electronics is to fabricate trilayer SIS Josephson Junctions. The major obstacle to achieving this goal is the large anisotropy of cuprate superconductors of the type referenced above, which results in a very short coherence length in the direction perpendicular to the CuO.sub.2 layers, as well as in generally small critical current, j.sub.c.perp., in that direction. The structural cause of at least a major part of this anisotropy is the existence of so-called "blocking layers" such as the Bi--O layer in Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8 (e.g., Beyers)
It is for that reason that a substantial interest has been generated by the first successful synthesis of (Sr,Ca)CuO.sub.2. This so called "infinite layer" cuprate, also known as the "parent compound" of cuprate superconductors, was synthesized in 1988 at the AT&T Bell Laboratories (Siegrist). This compound has no "blocking layers". However, its transport properties were disappointing, in that the material was found to be semiconducting and showed no traces of superconductivity.
Several Japanese groups have investigated this material, and there have been some reports of superconductivity in the material in the popular press. So far, the claims failed to be confirmed in other laboratories.
More recently, data on a (Sr,Ca)CuO.sub.2 thin film which showed resistance that at first increased with decreasing temperature in a semiconducting like-manner, but then turned over to decrease below about 60-80 K, has been reported. However, conductor resistance never reached zero, i.e., the samples were not completely superconducting (Kawai). The composition of the presumed minority superconducting phase was not identified.